The present invention relates generally to a method and apparatus for controlling the operation of a liquid dispensing system, and more particularly, to a method and apparatus for measuring and controlling the amount of viscous material dispensed from a dispensing system.
There are several types of prior art dispensing machines used for dispensing metered amounts of liquid or paste for a variety of applications. One such application is in the assembly of surface mount printed circuit boards, wherein adhesive liquid is dispensed in precise, predetermined locations on a circuit board. The adhesive liquid is used for connecting components to the circuit board. Another application of dispensing machines is in dispensing viscous material used for encapsulating integrated circuit chips and/or for under filling flip integrated circuit chips. The dispensing machines are generally required to run continuously to achieve a high throughput, and are also required to achieve a high degree of accuracy and repeatability (i.e., be able to dispense substantially identical dots with a very small tolerance or variability between dots). The dispensing systems described above include those manufactured by Speedline Technologies, Inc., the assignee of the present invention, and distributed under the name XYFLEX(trademark).
As semiconductor packaging technology advances, so too does the need for better and more accurate fluid dispensing technology to support this application. Manufacturers who use dispensing systems to encapsulate and underfill any of a variety of semiconductor packages demand ever more accurate and repeatable means for controlling the dispensing process. In one prior art dispensing system, the weight of material dispensed by the system is periodically measured by a scale during calibration routines, and the dispensing system includes a feedback system to adjust the quantity of fluid dispensed by the dispensing system, so that the weight of the material dispensed is controlled.
In some prior art dispensing systems, such as that disclosed in U.S. Pat. No. 5,906,682 to Bouras et. al, which is incorporated herein by reference, the addition of a weight scale to the dispensing process improves the accuracy and repeatability of the process by measuring the actual material flow rate being achieved, and adjusting the dispenser""s traverse speed as necessary to compensate for any long term variations. Inherent in this approach is the assumption that the flow rate is constant over the short term. However, in reality, fluid flow is seldom constant. Certainly the steady state material delivery rate cannot be achieved instantaneously, nor can the positioning system be accelerated or decelerated instantaneously. These nonlinear transitions result in discrepancies between predicted and actual material amounts. In embodiments of the present invention, to overcome these shortcomings, a different approach has been taken; the presence of these nonlinearities is acknowledged and their effects is captured by duplicating them during weight scale sample dispensing.
In one aspect, the present invention is directed to a system for dispensing material onto a substrate. The system includes a positioning system, a dispensing element coupled to the positioning system to move the dispensing element over the substrate to dispense material on the substrate in a predetermined pattern, the dispensing element having a metering device that controls a quantity of material that is dispensed from the dispensing element, a calibration device that receives material from the dispensing element during a calibration routine of the dispensing system, and a controller, coupled to the positioning system, the dispensing element and the calibration device to control operation of the system, wherein the controller is constructed and arranged to control the positioning system and the dispensing element such that the dispensing element is moved and controlled according to a calibration pattern to dispense material onto the calibration device during a calibration routine, and wherein the calibration pattern is representative of the predetermined pattern.
The system may be constructed and arranged such that movement of the positioning system is coordinated with dispensing from the dispensing element to provide a substantially uniform line of dispensed material on the substrate. The calibration device may be constructed and arranged to determine a quantity of material dispensed during a calibration routine, and the quantity may be compared with a target quantity of material to determine an error value. The controller may be constructed and arranged to apply a scale factor to the predetermined pattern to obtain the calibration pattern to reduce the distance traveled by the pump during the calibration routine to maintain the pump over the calibration device. The scale factor may be applied to the speed of movement of the dispensing system during a calibration routine such that the material dispensed during a calibration routine is substantially the same as that dispensed onto a substrate. The system may be constructed and arranged to adjust a rate of delivery of the metering device when the error value is greater than a predefined value. The system may be constructed to adjust a speed of movement of the pump when the error value is greater than a predefined value.
Another aspect of the present invention is directed to a method of calibrating a dispensing system that dispenses material onto a substrate according to a predetermined pattern, the dispensing system having a dispensing pump that dispenses material and a gantry system that controls movement of the pump over the substrate and over a calibration system. The method includes steps of (a) moving the pump over the calibration system, (b) dispensing a quantity of material from the pump while the pump is moved by the gantry system according to a calibration pattern that is representative of the predetermined pattern, (c) determining the quantity of material dispensed, (d) comparing the quantity of material dispensed with a target quantity, and (e) adjusting characteristics of the dispensing system when a difference between the quantity of material dispensed and the target quantity is greater than a predetermined tolerance. Steps (a) through (e) may be repeated prior to dispensing on a substrate until the difference is less than the tolerance. The method may further include a step of applying a scaling factor to the predetermined pattern to reduce the distance traveled by the pump to maintain the pump over the calibration system during a calibration routine. The scaling factor may be applied to the gantry system to reduce the speed of movement of the pump during a calibration routine such that the material dispensed during a calibration routine is substantially the same as that dispensed onto a substrate.
Another aspect of the present invention is directed to a system for dispensing a material onto a substrate. The system includes a positioning system, a dispensing element coupled to the positioning system to move the dispensing element over the substrate to dispense material on the substrate in a predetermined pattern, the dispensing element having a metering device that controls a quantity of material that is dispensed from the dispensing element, a calibration device that receives material from the dispensing element during a calibration routine of the dispensing system, means for moving the dispensing element according to a calibration pattern that is representative of the predetermined pattern to dispense material onto the calibration device during a calibration routine, and means for determining a quantity of material dispensed during a calibration routine.
The system may further include means for determining a difference between the quantity of material dispensed with a target quantity, and means for adjusting characteristics of the system to reduce the difference.
Yet another aspect of the present invention is directed to a method of calibrating a dispensing system that dispenses material onto a substrate according to a predetermined pattern, the dispensing system having a dispensing pump that dispenses material and a gantry system that controls movement of the pump over the substrate and over a calibration system. The method includes steps of (a) moving the pump over the calibration system, (b) dispensing a quantity of material from the pump while the pump is held at a fixed position over the calibration system and the pump is controlled to follow a dispensing calibration pattern that is representative of a dispensing pattern of the pump for the predetermined pattern, (c) determining the quantity of material dispensed, (d) comparing the quantity of material dispensed with a target quantity, and (e) adjusting characteristics of the dispensing system when a difference between the quantity of material dispensed and the target quantity is greater than a predetermined tolerance.